1.Field of the Invention
The present invention relates to a total reflection type X-ray diffraction micrographic method and an apparatus for implementing the same method, and in particular, to a total reflection type X-ray diffraction micrographic method and apparatus suitable for detecting crystal defects present on and within the surface of a semiconductor wafer.
2. Description of the Related Art
In a semiconductor wafer such as a single crystalline silicon wafer, crystal defects present therein or thereon (for example, voids, interstitial atoms, dislocations, random stacking, depositions, segregations or the like) can exert adverse effects on the characteristics of a semiconductor device produced from this semiconductor wafer. In view of this problem, numerous methods have been developed to detect and evaluate the crystal defects present in the interior or on the surface of semiconductor wafers.
As one of such methods, there has been available a method called X-ray diffraction microscopy or X-ray topography which utilizes a diffraction phenomenon of X-rays. FIG. 1 is a layout plan view illustrating an arrangement implemented when a silicon (100) wafer is measured in accordance with this method. Incident X-ray beam 51, which is generated by an X-ray tube or the like and is formed into a thin and elongated beam by using a slit, is made monochromatic by means of a monochromater comprising spectroscopic analyzing crystal 52. Here, the glancing angle of incident X-ray beam 51 is made small so that it may come incident to the surface at an angle close to the surface of analyzing crystal 52 and, further, the orientation of analyzing crystal 52 is appropriately selected. As a result, monochromatic X-ray beam 53 emitted from analyzing crystal 52 becomes a widely spaced parallel light beam with an emitting angle which is nearly perpendicular to the crystal surface, and thereby comes incident to a wide area of the surface of silicon (100) wafer 54, the sample to be evaluated. The X-ray beam which enters silicon (100) wafer 54 is diffracted in accordance with Bragg's effect within wafer 54 and emitted from wafer 54. Diffracted X-ray beam 55 then strikes photographic film 56. If no crystal defects exist on or within wafer 54, the diffracted image formed on photographic film 56 is uniform, and, if otherwise, some turbulence will be apparent in this diffracted image. Therefore, the crystal defects existing on and within sample wafer 54 can be detected and evaluated by exposing film 56 to diffracted X-ray beam 55, developing exposed film 56, and finally, examining the diffraction image on the developed film by means of a microscope or the like. According to this method, the incident depth of the monochromatic X-ray beam which comes incident to the sample is on the order of several micrometers, and this range allows extensive information to be obtained regarding the sample as viewed in the direction of its depth.
In recent years, numerous semiconductor devices having a shallow junction have been in practical use. It is important to obtain information regarding crystal defects in the close neighborhood of the surface (within several nanometers in depth) of the semiconductor wafers making up these devices. However, according to the above-described conventional X-ray diffraction micrography, the incident depth of the X-ray beam into the specimen is too great to obtain the information regarding the close neighborhood of the surface.